Hot-formed metal structural parts are widely used in the automotive industry, in particular in crash-relevant regions of the bodywork subjected to high transverse stresses. Thus, B pillars and B pillar reinforcements are frequently made of high-strength, hot-formed manganese-boron steel. High stretching resistances and tensile strengths in the structural component can be achieved by processing such materials in a hot forming process, so that the necessary sheet metal thickness can be considerably reduced compared to conventionally produced steel structural components and in this way a contribution to light-weight construction and thus to CO2 reduction can be achieved. The disadvantage of completely hot-formed metal structural components is that the elongation at fracture of a hot-formed metal structural component is relatively low. Hot-formed metal structural components can therefore be successfully used in transverse-stressed regions, since here the high strengths, in particular the yield strength, avoid a buckling of the metal structural components. Hot-formed metal structural components cannot, however, be used in the case of longitudinally stressed metal structural components, such as for example longitudinal members, since the low elongation at fracture would not allow a uniform folding of the metal structural components and the consequence would be a failure of the material following a relatively low energy absorption.
In DE 102 56 621 B3 a sheet bar is heated under varying conditions in a straight-flow furnace, so that on account of the different material temperatures different strengths in the metal structural component are obtained after the forming. In this method the sheet bar is tempered differently when it passes through two furnace chambers, so that different structural regions are established in the hardening process. This method has the disadvantage that only two to three different zones as regards strength and elongation at fracture can be achieved in the metal structural component. These can, furthermore, be formed only in the throughflow direction of the sheet bar. The throughflow direction of a steel part or sheet bar corresponds as a rule to the largest longitudinal dimension of the steel part or sheet bar.
DE 10 2006 019 395 A1 discloses a device and a method for the forming of sheet bars of high strength and super-high strength steels, with the aim of using hot-formed metal structural components also in longitudinally-stressed regions. The method is characterised in that the forming tool for the hot forming comprises tempering means with which a steel part can be tempered in different temperature zones during the forming to different, predetermined temperature values. In this way it is possible locally to influence the microstructure in the metal structural component, so that metal structural components with location-dependent material properties can be produced. Location-dependent material properties are understood to mean that the material properties are different in at least two partial regions of the metal structural component. The different types of structure are achieved by different cooling rates of the material. The forming tools with the means for tempering are however relatively complicated to produce and are therefore expensive.
The present invention is therefore based on the technical objective of providing a method and a device for producing a metal structural component, which permits a local adjustment of the structure in the metal structural component and at the same time is inexpensive and simple to implement.